Radiosurgery, also referred to as radiation treatment, typically involves delivery of a predetermined dosage of radiation to a target region in a patient to treat a tumor within the target region. Typically, a high dosage of radiation is delivered to the target region while the rest of the patient's body may be exposed to a relatively low level of radiation. If a high dosage of radiation is mistakenly delivered outside of the target region, not only the tumor may not be treated properly, healthy tissue outside of the target region may be damaged by the mistakenly delivered radiation. Thus, accurate determination of the location of the target region during treatment delivery is crucial in providing safe and effective radiation treatment to the patient. The location of the target region during treatment delivery may also be referred to as the intra-operative location of the target region in the following discussion.
Although a patient undergoing radiation treatment may be substantially immobilized, there are nevertheless movements of the patient caused by respiration of the patient. Such movements are particularly significant in certain parts of the patient's body, such as the lungs, the diaphragm, etc., such that the accuracy in radiation delivery to a target region within these parts may be affected. In order to accurately track the location of a target region that moves responsive to respiration, various techniques have been developed, including irradiation during breath-hold, gating techniques, and active tracking of the target region.
Irradiation during breath-hold requires the patient undergoing radiosurgery to hold his/her breath in a particular way. Typically, the patient has to be trained by verbal commands in order to achieve nearly full vital capacity during breath-hold. However, the above technique is complicated and inconvenient to the patient because training is required. Further, the above technique is susceptible to error because the patient may easily miss a verbal command, and thus, unintentionally changing the duration of the breath-hold. Alternatively, the patient may breathe through a mouthpiece connected to a portable system for coordinating treatment with the patient's respiration. The system may measure the lung volume and display relevant data on a monitor. If the pre-specified breathing volume is reached, a valve blocks airflow for a predefined time span. Irradiation is performed during breath-hold. Many patients can tolerate a breath-hold of about ten to thirty seconds. Although training may not be required under this approach, nevertheless, it is still uncomfortable for the patient to hold his/her breath repeatedly during treatment.
Another conventional fiducial-less radiosurgical technique is gating. To implement gating, one or more sensors, which may include sensors internal and/or external to the patient's body, collect information about the current state of the respiration of the patient. Each time a target region moves out of a predefined window of a particular sensor, the radiation source is switched off. Although gating may be more comfortable for the patient than irradiation during breath-hold, the treatment time of gating may significantly increase due to interruption of treatment caused by frequent switching off of the radiation source.
Active tracking of the target region is another conventional fiducial-less radiation treatment technique. When the target region moves away from a predetermined location, instead of switching of the radiation source, the direction and/or location of the radiation source is adjusted so that the radiation beam substantially moves with the target region. Thus, the location of the target region has to be tracked during treatment. Conventionally, fiducials are used to track the location of the target region during treatment.
Fiducial is a term derived from surveying, meaning a reference marker. Here, a fiducial is a radio opaque marker that is visible to an imaging system of the treatment delivery system. Fiducials may be attached to or implanted into a patient's body to allow surgeons to track the intra-operative location of the target region during treatment delivery.
However, fiducial-based tracking may be undesirable for patients because of various reasons. It is typically uncomfortable for the patients to have fiducials implanted into their bodies. Further, complications may result from the implantation of fiducials. Although attaching fiducials to a patient's skin may be easier and more comfortable for the patient and less risky, the accuracy in tracking the volume of interest in the patient's body may be compromised because the fiducials attached are farther away from the target region and thus, the intra-operative movement of the fiducials and/or intra-operative locations of the fiducials may not correlate well with the intra-operative locations of the target region.